The present invention relates to a method for controlling a power source of a forestry machine.
Various forestry machines, such as forwarders and harvesters, are known for carrying out mechanized harvesting. A forestry machine typically comprises a base provided with wheels or rolls and capable of moving on the ground. The base is provided with a cabin and work devices required for each particular case. Such a work device consists of, for example, a boom system, such as a crane or a loader. The end of the boom system is provided with a handling device supported by the boom system in each particular case, with which handling operations are performed for the timber harvested from a forest.
Various harvester heads are moved and used at the end of a boom system in a felling machine, i.e. a harvester, which harvester heads are capable of handling tree trunks in a versatile manner. A harvester head is used for at least felling, delimbing, measuring and cutting the trunk to be handled in a desired manner. On the other hand, various handling devices for performing energy wood harvesting and clearing, such as fuel wood grabs, are known which do not necessarily comprise means required for delimbing or feeding, for instance.
Most of the functions of trunk handling in forestry machines are nowadays hydraulically implemented. For example sawing, feeding, and moving delimbing knives and feed rollers to the open and closed position are examples of individual harvester head functions. Typical boom system functions, in turn, include lifting, bending and turning a boom system, and guiding a telescopic extension in the boom system in and out.
A forwarder is a forestry machine specifically intended for short-distance haul of timber, capable of collecting and transporting the pieces of trunk handled by a harvester, for instance, in their load space to the border of the cutting area for onward transport.
Also what are called dual or combi machines are known that are capable of performing tasks of both a harvester and a forwarder.
In the above-mentioned forestry machines, the primary power source has conventionally been a diesel engine, with which most of the mechanical, electric or pressure medium transmitted power is provided. Such a primary power source, in turn, typically utilizes one or more hydraulic pumps to pressurize the pressure medium. From this primary power source, power and performance can be transmitted also in ways other than hydraulically, for example for the requirements of a traction transmission of a forestry machine or for the need of the work and handling devices in it.
The control of a diesel engine constituting the primary power source in forestry machines has conventionally been implemented in a very simple manner. The control of the power source thus aims at a substantially constant rotative speed, whereby its operation is usually controlled by means of for example a control device, i.e. a controller, in connection with the diesel engine.
However, not even in most cases has it been possible with the control of the power source to avoid situations where the performance of the power source has momentarily been too small. Such a situation typically causes a dip in the rotative speed of the power source, which easily slows down successful implementation of the function to be carried out, or makes it more difficult. Particularly saw cut operations of the trunk after felling a tree are of such a nature that the slowing down of the function may result in significant losses in the form of cutting flaws on the trunks. Modern diesel engines enable, however, a very versatile and quickly reacting control of a power source. The output magnitudes of the engine, such as rotative speed, torque and power production capacity or availability, can be affected significantly by such control.
Thus, solutions are also known where the primary power source of a forestry machine is controlled more actively than before. One solution of this kind is presented in patent publication FI 111183. This publication discloses a forestry machine in which the wood to be handled in it is assessed in an automated and anticipatory manner trunk-specifically. The purpose of the assessment is to achieve continuous information on the power level required by one or more wood handling steps in such a way that the operation of the primary power source of a forestry machine could be automatically optimized trunk-specifically by affecting control parameters of the power source to achieve as optimal efficiency as possible.
On the other hand, it is known that along with the latest engine technology and restricted emission regulations, for instance the capability of diesel engines to respond to an increase in a great and rapid stepwise load has even deteriorated compared to earlier engine technology provided with a mechanical injection pump and injection control. Presently, diesel engines used in forestry machines are usually turbo-charged engines provided with an electrically controlled injection system, the power and torque of which are, to a great extent, based on turbo charging. In other words, the amount of fuel injected to an engine only lightly loaded is small, and also the boost pressure is low. When the engine is then unexpectedly loaded, the power production capacity of the engine does not necessarily correspond immediately to the nominal power of the engine, according to which the power source to a power device is usually rated.
It has been observed, however, that the power demand of the forestry machine functions is not always dependable on the trunk-specific properties of the wood under handling but on the forestry machine functions and their implementation as such. This is partly due to the low efficiency of the hydrostatic power transmission used in a forestry machine. Particularly, this is the case when the trees to be handled are small in size.